1. Field of the Invention
The present invention relates to processes for the production of a printed circuit board and, more particularly, to processes for facilitating the electrodepositing of closely compacted conductive patterns in an economic and efficient manner.
2. Description of Related Art
A large number of processes and resultant printed circuit boards have been proposed in the last 35 years to meet the demands of the electronics industry. The miniaturization of electronic components and the reduction in size of the supporting printed circuit boards have imposed additional constraints on manufacturers of modern printed circuit boards. Various forms of clad and strip processing techniques have been suggested and utilized in the manufacturing of printed circuit boards. An example of one technique and a summary of other prior art techniques are set forth in U.S. Pat. No. 4,080,513.
In a conventional process for manufacturing a printed circuit board, a number of independent conductive strips or patterns are isolated on an insulating substrate. These patterns of independent strips must be electrically interconnected to facilitate a electroplating step of depositing desired conductive material on certain areas of the substrate. This can be accomplished by temporarily connecting the desired conductive patterns with a secondary pattern of plating lead layers to carry the plating current. This secondary plating lead layer, however, is only necessary as an intermediate step in the production of the printed circuit board. The desired primary conductive strips must again be electrically isolated to achieve the desired conductive interconnection between the electronic component parts that are to be mounted on the printed circuit board. Thus, it is known that the electrical interconnection between the independent primary conductive pattern must be removed before the printed circuit board is finished.
A prior art method of removing or isolating the independent electrical components from each other is disclosed in FIG. 11, wherein the pattern of plating lead layers are physically cut off by drilling holes in the printed circuit board. Thus, in FIG. 11 the circled portions B indicate drilled holes where the electrical connection between the independent primary conductive patterns has been effectively removed. As can be readily appreciated, by simply cutting off the pattern of plating lead layers with a hole drilling technique, there still remain cut off sections of the pattern of plating lead layers which are exposed and remain in contact with the desired independent conductive segments of the printed circuit board. Thus, there remains a risk that these independent components may be shorted out or connected with another cut off section through unintentional contact with conductive material to bridge the drilled hole.
An additional problem occurs in any production process desiring to produce a printed circuit board of an extremely high density. In such a design, the space between the respective conductive lines represents a distinct limitation on the compacting of the circuit pattern. Utilizing a plating lead layer to interconnect the independent conductive segments while permitting a drilling or cutting off of the lead line, which is part of the finishing step, clearly creates a significant design problem. The deposited primary conductive pattern must be designed so that any essential component of conductive material in the desired final pattern should not be endangered in being cut off through any drilling step. If the design suggests that the plating lead layer must be positioned in a space between desired conductive segments which is smaller than the diameter of a drill, for example, as shown by circle A in FIG. 11, an alternative step, such as a grinding or an abrading step, would be necessary.
In one conventional process for producing a printed circuit board, a pattern of a primary electroconductive layer and a pattern of a plating lead layer are created on an insulating substrate. This is accomplished, for example, by etching a surface of a copper clad laminate substrate. Subsequently, predetermined portions of the final conductive pattern are plated electrically to deposit an additional conductive material. Finally, any interconnecting patterns of plating lead layers are removed by drilling or grinding to provide the final configuration of the printed circuit board.
There is still a desire in the field of manufacturing printed circuit boards to improve the production processes in an efficient manner to produce highly accurate and concisely defined printed circuit board conductive patterns while eliminating the possibility of short circuits.